In June 2023, we will enter the last phase of a $1 billion project to repair the longest tunnel in the world—the Delaware Aqueduct. We will be connecting a newly constructed 2.5-mile bypass tunnel to structurally sound portions of the existing Delaware Aqueduct, permanently conveying water around a leak. To make this connection, we will shut down the Delaware system for eight months, starting in October 2023.
The Delaware Aqueduct begins at Rondout Reservoir in Ulster County and conveys about 50 percent of New York City’s drinking water every day. This repair project, as well as water supply operations throughout the shutdown, have been in the planning process for more than 20 years and will have impacts on the supply system’s reservoir levels as well as some recreation activities in the City’s watersheds.
To learn about New York City’s water supply systems, visit Water Supply. For up-to-date reservoir levels and release rates, visit Reservoir Levels.
The start of the shutdown is being carefully timed to coincide with the end of peak summer demand on the water system. An unusually dry and hot summer before the planned shutdown—such as occurred in 2022—could delay the project. Unforeseen complications and computer modeling that predicts reservoir refill probabilities will drive all “go-no-go” decisions leading into and throughout the shutdown. For real-time updates and outreach event information, please follow our NYC Watershed Facebook page.
Over the past decade, we have worked on several projects to ensure New York City will have a reliable supply of drinking water during the shutdown period: see Final Concrete Lining on Bypass Tunnel Completed, Final Steel Segment Lowered into Bypass Tunnel, Catskill Aqueduct Rehabilitation, and Bypass Tunnel Excavation Complete for more details.
Impacts on the Delaware System
The Delaware system, which includes Cannonsville, Pepacton, Neversink, and Rondout reservoirs in Sullivan, Ulster, and Delaware counties, will be shut down in October 2023 prior to the final bypass connection. Rondout Reservoir serves as the central collecting reservoir for the three other Delaware system reservoirs, but during the shutdown, it will only receive water from its 95-square-mile watershed. In preparation for the shutdown, we installed three siphons as an extra method to remove water from Rondout Reservoir, which will help manage surface water levels and reduce the likelihood that water will pass through its spillway.
Prior to the shutdown period, all four Delaware system reservoirs will be drawn from more than usual. Depending on the amount of precipitation, each reservoir is expected to be drawn down from capacity by 30 percent or more, creating a substantial void that will help to reduce storm impacts in the region. During the shutdown period, Delaware system reservoirs will refill and continue downstream releases into the Delaware River.
The shutdown should not impact public recreational uses of the lands and water bodies of the Delaware System. To monitor recreation updates, visit: Recreation.
For more information, download the Delaware Watershed Factsheet for the Delaware Aqueduct Shutdown.
Impacts on the Catskill System
The Catskill system, comprised mainly of Ashokan and Schoharie reservoirs in Ulster, Delaware, Greene, and Schoharie counties, typically provides about 40 percent of the city’s water supply and will become the primary source of the city’s water supply throughout the shutdown. The Catskill systems near 160-billion-gallon storage capacity west of the Hudson River is expected to be minimized before the October shutdown of the Delaware Aqueduct, and surface levels of Ashokan will likely appear lower during winter 2024 while the Delaware is shutdown. Regulated releases from Ashokan into the Esopus Creek will continue throughout the Delaware shutdown as per the Interim Release Protocol.
The shutdown should not impact public recreational uses of the lands and water bodies of the Catskill System. To monitor recreation updates, visit: Recreation.
For more information, download the Catskill Watershed Factsheet for the Delaware Aqueduct Shutdown.
Impacts in the Croton System
The Croton system is comprised of 12 interconnected reservoirs and three controlled lakes in Westchester and Putnam counties, and typically provides about 10 percent of the city’s water supply. During the shutdown, the system will ramp up to provide 30 percent of the city’s water supply. Several of the reservoirs will be drawn down more substantially than usual, and large pumping stations will be used to push Croton system water into the lower portion of the Delaware Aqueduct, which will remain operational from West Branch Reservoir to Kensico Reservoir and into the city’s distribution system. Water in West Branch and Boyds Corner reservoirs will be held as reserve during the shutdown period.
During the shutdown we will pump an average 150 million gallons a day (mgd) from Croton Falls Reservoir into the lower Delaware Aqueduct to help augment the City’s supply. There will also be the regulated minimum downstream releases of 20 mgd from Croton Falls and 30 mgd from Croton Falls Diverting reservoirs.
Downstream releases from Bog Brook, East Branch, and Middle Branch reservoirs will increase. We will also pump up to 60 mgd from Cross River Reservoir into the lower Delaware Aqueduct for additional augmentation of the City’s supply system. Downstream releases from the Cross River Reservoir will be reduced to the regulated minimum of 5 mgd.
We will keep a minimum regulated release of 5.5 mgd from New Croton Reservoir into the Croton River from October 2023 to March 2024, and with a variance will maintain a release flow of 11 mgd in April and May instead of the regulated minimum of 75 mgd.
The shutdown should not impact public land recreational use, but boating and fishing activities throughout the Croton system reservoirs in Westchester and Putnam counties are expected to change. Ice fishing will be restricted on several reservoirs during winter 2023/24 and some reduced downstream releases of water to various rivers and streams could inhibit stream fishing in several areas. To monitor boating and fishing recreation updates, visit Boating for Anglers and Fishing.
For more information, download the Croton Watershed Factsheet for the Delaware Aqueduct Shutdown.